Reducing the impact of earthquakes

Working together, researchers in Japan and Australia are getting better at predicting the areas most at risk from earthquakes.

They are also working together on ways to determine, within seconds of a warning, the scale and likely impact of an earthquake. Rapid detection and warning systems combined with smart engineering saved many lives in the Great Japanese Earthquake of 2011. But the earthquake and the resulting tsunami were much bigger than geological modelling suggested. The reasons for that might be found in deep history.

Mapping the hazard

Big earthquakes may be separated by centuries or millennia. But earthquake hazard maps are based on information gathered since 1900 when modern seismographs came into use. It’s difficult to model events happening over millennia when you have not got deep historical information.

University of Sydney researchers led by Professor Dietmar Muller believe they can push beyond that limitation. Large earthquakes are generally associated with subduction zones—where tectonic plates collide and one pushes under the other. The Sydney team has shown that areas where subduction zones intersect with oceanic fracture zones are particularly dangerous and they have created a global hazard map for giant subduction earthquakes.

The map helps explain why the Great East Japan Earthquake happened and identifies other high risk areas.

Professor Brian Kennett at the Australian National University has worked with multiple images from “seismic tomography” which produces 3-D models of the Earth and has shown that the zone of initiation of the 2011 event has unusual properties, based on observations of earthquakes from around the globe. Similar results have been obtained independently by researchers at Tohoku University and Kennett has also collaborated with researchers at Kyoto University on a review of the properties of the 2011 event. Professor Kennett has also worked with the University of Tokyo’s Earthquake Research Institute for over 20 years to improve earthquake simulations using supercomputing.

Looking back in time

The landscape of the Sendai region of Japan retains evidence of past tsunamis. Professor James Goff and Dr. Catherine Chagué-Goff, with colleagues from the University of New South Wales, ANSTO, and Tohoku University have been reading the evidence left by the 2011 tsunami.

Layers of sand in sediment can indicate past tsunamis. But for nearly half of the 5.6 kilometres of the tsunami’s sweep over the Sendai Plain, it left no sand debris. Up to 4.6 kilometres inland it left finer sediments behind. But it kept going, damaging crops and leaving salty soil for a further kilometre. That has led the team to reinterpret the strength of past tsunamis on the Sendai plain, which occurred in 869, and earlier around 2,000 and 2,700 years ago.

A more accurate reading of the geochemical history of these past tsunamis will also help them interpret evidence of past tsunamis across the Pacific and contribute to a better measure of the risk of future tsunamis. The team has created databases of past Australian and New Zealand tsunamis. Now they’re working with Tohoku University, Hokkaido University and the Japanese Nuclear Regulation Agency to create a similar database for Japan. And with their Tohoku colleagues they’re looking at less developed coastlines in the Pacific—on Hawaii and Chatham Island—for more evidence of the impact of earlier tsunamis. All this work will contribute to a better understanding of the risks across the Pacific Ocean nations.